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The Calvin Cycle
Or
the Dark Side of
Photosynthesis II
NOTE: ONLY WRITE DOWN THE SLIDES WITH THE
BLACK BACKGROUND!!! THEY ARE A SUMMARY OF
THE PREVIOUS SLIDES!
While the purpose of photosynthesis is for plants to make glucose from
carbon dioxide, but there is a second reason why plants do
photosynthesis- to make organic molecules from the PGAL skeleton.
A second function of the dark reaction is to make other
compounds needed by the plant.
#1, #2
There are environmental factors that can affect the rate of
photosynthesis.
1. Light intensity- At first an increase in the light intensity will result in
a corresponding increase in the rate of photosynthesis as the
photosystems become activated. Then as the photosystems become
saturated, an increase in light intensity will not increase the rate of
photosynthesis.
2. Temperature- At
first an increase in
temperature
results in an increase in the rate
of photosynthesis because the molecules are
moving faster, but at a higher temperature
the reaction rate decreases because enzymes
denature.
3. If a plant is given an increase in oxygen, the
rate of photosynthesis decreases because of
phenomenon of photorespiration.
Envrionmental factors that effect the rate of photosynthesis
1. Light intensity-An increase in light intensity will increase photosynthesis until it reaches the saturation of photosystems
#3, #4
2.Temperature-At first an increase in temperature will increase
the rate of photosynthesis but after a certain temperature the
enzymes denature and the plant cells are killed. (The plant is
being cooked)
3. Increasing the concentration of oxygen,
decreases the rate of photosynthesis
because of increase in photorespiration.
The enzyme that puts the CO2 onto
ribulose biphosphate is rubisco.
Somtimes rubisco can make a mistake
and put oxygen on to ribulose
biphosphate. This happens when the
concentration of oxygen gas is greater
than carbon dioxide. This happens
when the plant is water stressed and the
stomates are closed.
Gas exchange takes through pores on the bottom of the plant
called stomates. Guard cells regulates these openings but as gas
exchange occurs water leaves the stomates via transpiration.
When a plant becomes water stressed, stomates close to conserve
water. water, but this will stop gas exchange. This will increase
the O2 and decrease CO2. Photorespiration begins. C3
photosynthesis is a plant that does the Calvin cycle and the light
reaction. There are plants that modify C3 photosynthesis by
adding an additional pathway-
The enzyme that puts the CO2 onto ribulose
biphosphate is rubisco. Rubisco can make a mistake of
putting O2 on ribulose biphosphate. This happens
when the concentration of oxygen gas is greater than
carbon dioxide. This occurs when the plant is water
stressed and the stomates (pores on bottom of leave)
are closed. Guard cells open and close stomates.
This stops transpriation (water loss through stomates)
but also stops gas exchange. This increases the O2 and
decreases CO2. Photorespiration begins.
C3 Photosynthesis= Light reaction + Calvin Cycle
There are plants that modify C3 photosynthesis by
adding an additional pathway#5, #6,#7
The leaf of a C3 plant. Chloroplasts are located in the
palisade and spongy mesophyll. There are no chloroplasts
in the bundle sheath cells.
#8
The leaf of a C3 plant. Chloroplasts are located in
the palisade and spongy mesophyll. There are
no chloroplasts in the bundle sheath cells.
C4 photosyntheis includes the light reaction, the Calvin cycle
and the Hatch-Slack pathway. These C4 plants also have a
different anatomy. This Hatch-Slack pathway is able to deliver
dwindling supplies of CO2 when the stomates are closed. The
enzyme that combines the CO2, combines it with a three carbon
compound to form a four carbon compound. This enzyme
does not make a mistake like rubisco.
The leaf of a C4 plant. There are no
palisade mesophyll cells. Instead there
is a layer of mesophyll around the the
bundle sheath cells. Chloroplasts are
located in the these mesophyll and
spongy mesophyll..
C4 photosyntheis includes the light reaction, the Calvin
cycle and the Hatch-Slack pathway. These C4 plants also
have a different anatomy. This Hatch-Slack pathway is able
to deliver dwindling supplies of CO2 when the stomates are
closed. The enzyme that combines the CO2 combines it
with a three carbon compound to form a four carbon
compound, does not make a mistake like rubisco.
The leaf of a C4 plant. There are
no palisade mesophyll cells.
Instead there is a layer of
mesophyll around the the bundle
sheath cells. Chloroplasts are
located in the these mesophyll
and and spongy mesophyll.
Another variation of photosynthesis is CAM (crassulacean
acid metabolism). These are succulent plants. Because of
the intense heat and arid conditions, these plants only open
up their stomates at night for gas exchange. The CO2 is
converted to organic acid and stored until the day. During
day stomates are closed and the cell releases the CO2 from
the organic acid.
Another variation of photosynthesis is CAM
(crassulacean acid metabolism). These are
succulent plants. Because of the intense heat and
arid conditions, these plants only open up their
stomates at night for gas exchange. The CO2 is
converted to organic acid and stored until the day.
During day stomates are closed and the cell
releases the CO2 from the organic acid.